Biosynthesis of Glucose:
Gluconeogenesis is the process of synthesizing glucose
from non-carbohydrate sources. The starting point of gluconeogenesis
is pyruvic acid, although oxaloacetic acid and dihydroxyacetone
phosphate also provide entry points. Lactic acid, some amino
acids from protein and glycerol from fat can be converted into
glucose. Gluconeogenesis is similar but not the exact reverse
of glycolysis, some of the steps are the identical in reverse
direction and three of them are new ones. Without going into
detail, the general gluconeogenesis sequence is given in the
graphic on the left.
Notice that oxaloacetic acid is synthesized from pyruvic acid
in the first step. Oxaloacetic acid is also the first compound
to react with acetyl CoA in the citric acid cycle. The concentration
of acetyl CoA and ATP determines the fate of oxaloacetic acid.
If the concentration of acetyl CoA is low and concentration of
ATP is high then gluconeogenesis proceeds. Also notice that ATP
is required for a biosynthesis sequence of gluconeogenesis.
Gluconeogenesis occurs mainly in the liver with a small amount
also occurring in the cortex of the kidney. Very little gluconeogenesis
occurs in the brain, skeletal muscles, heart muscles or other
body tissue. In fact, these organs have a high demand for glucose.
Therefore, gluconeogenesis is constantly occurring in the liver
to maintain the glucose level in the blood to meet these demands.
Link to: Interactive
Gluconeogenesis (move cursor over arrows)
Jim Hardy, Professor of Chemistry, The University of Akron.
Link to Rodney Boyer - Gluconeogenesis
|Quiz: How many pyruvic acid molecules are required
to make glucose?